According to historian Jeremy Belknap, the area was called Wecohamet by native AbenakiIndians. The first known European to explore the region was Martin Pring from Bristol, England, in 1603. Settled in 1623 as Hilton's Point by brothers William and Edward Hilton, London fishmongers,[3] Dover is the oldest permanent settlement in New Hampshire, and the seventh oldest in the United States. It is one of the colony's four original townships, and once included Durham, Madbury, Newington and Lee. It also included Somersworth and Rollinsford, together which Indians called Newichawannock after the Newichawannock River, now known as the Salmon Falls River.

The Hiltons' name survives today at Hilton Park on Dover Point, located where they landed near the confluence of the Cochecho and Bellamy rivers with the Piscataqua. They had been sent from London by The Company of Laconia, which intended to establish a colony and fishery around the Piscataqua. In 1631, however, it contained only three houses.

In 1633, the Plantation of Cochecho was bought by a group of English Puritans who planned to settle in New England, including Viscount Saye and Sele, Baron Brooke and John Pym. They promoted colonization in America, and that year Hilton's Point was the arrival point of numerous immigrant pioneers, many from Bristol. They renamed the settlement Bristol. Atop the nearby hill, the settlers built a meeting house, surrounded by an entrenchment, to the east of which they built a jail.

Settlers felled the abundant trees to build log houses called garrisons. The town's population and business center would shift from Dover Point to Cochecho at the falls, where the river's drop of 34 feet (10 m) provided water power for industry. Indeed, Cochecho means "the rapid foaming water." Major Richard Waldron settled here and built a sawmill and gristmill.

At the end of King Philip's War, a number of aboriginal natives fleeing from the Massachusetts Bay Colony militia took refuge with the Abenaki tribe living in Dover. The Massachusetts militia ordered Waldron to attack the natives and turn the refugee combatants over to them. Waldron believed he could capture the natives without a pitched battle and so on September 7, 1676 invited the natives—about 400 in total, half local and half refugees—to participate in a mock battle against the militia. It was a trick; after the natives had fired their guns, Waldron took them prisoner. He sent both the refugee combatants and those locals who violently objected to this forced breach of hospitality to Boston, where seven or eight were convicted of insurrection and executed. The rest were sold into slavery in "foreign parts",[citation needed] mostly Barbados. The local Indians were released, but never forgave Waldron for the deception, which violated all the rules of honor and hospitality valued by the natives at that time. Richard Waldron would be appointed Chief Justice for New Hampshire in 1683.

Thirteen years passed and settlers believed the incident had been forgotten when King William's War began and members of the newly formed Wabanaki Confederacy arrived. When citizens spoke their concern to Waldron, he told them to "go and plant your pumpkins, and he would take care of the Indians."[5] On June 27, 1689, two native women appeared at each of five garrison houses, asking permission to sleep by the fire. All but one house accepted. In the dark early hours of the next day, the women unfastened the doors allowing native men who had concealed themselves to enter the town. The now elderly Dover resident Richard Waldron was captured, and set out for special torture and mutilation. The Indians cut him across the belly with knives, each saying "I cross out my account." Five or six dwelling houses were burned, along with the mills. Fifty-two colonists, a full quarter of the entire population, were captured or slain.[5]

Located at the head of navigation, the falls of the Cochecho River helped bring the Industrial Revolution to 19th century Dover in a big way. The Dover Cotton Factory was incorporated in 1812, then enlarged in 1823 to become the Dover Manufacturing Company. In 1827, the Cocheco Manufacturing Company was founded (the misspelling a clerical error at incorporation), and in 1829 purchased the Dover Manufacturing Company. Expansive brick mill buildings, linked by railroad, were constructed downtown. Incorporated as a city in 1855, Dover was for a time a national leader in textiles. The mills were purchased in 1909 by the Pacific Mills of Lawrence, Massachusetts, which closed the printery in 1913 but continued spinning and weaving. During the Great Depression, however, textile mills no longer dependent on New England water power began moving to southern states in search of cheaper operating conditions, or simply went out of business. Dover's millyard shut down in 1937, and was bought at auction in 1940 by the city itself for $54,000. There were no other bids. The Cocheco Falls Millworks now has tenants including technology and government services companies, and a restaurant.[7][8]

According to the United States Census Bureau, the city has a total area of 29.0 square miles (75.2 km2), of which 26.7 square miles (69.2 km2) is land and 2.3 square miles (6.0 km2) is water, comprising 7.96% of the city.[1] Dover is drained by the Cochecho and Bellamy rivers. Long Hill, elevation greater than 300 feet (91 m) above sea level and located 3 miles (4.8 km) northwest of the city center, is the highest point in Dover. Garrison Hill, elevation approximately 290 ft (88 m), is a prominent hill rising directly above the center city, with a park and lookout tower on top. Dover lies fully within the Piscataqua River (Coastal) watershed.[10]

As of the census of 2010, there were 29,987 people, 12,827 households, and 7,059 families residing in the city. The city grew by 3,103 residents between 2000 and 2010, the largest numeric growth of any town or city in New Hampshire. The population density in 2010 was 1,123.1 people per square mile (433.3/km²). There were 13,685 housing units at an average density of 512.5 per square mile (197.8/km²). The racial makeup of the city was 90.6% White, 1.7% African American, 0.20% Native American, 4.6% Asian, 0.05% Pacific Islander, 0.6% some other race, and 2.3% from two or more races. Hispanic or Latino of any race were 2.2% of the population.[14]

There were 12,827 households, out of which 27.8% had children under the age of 18 living with them, 40.8% were headed by married couples living together, 10.3% had a female householder with no husband present, and 45.0% were non-families. 31.8% of all households were made up of individuals, and 9.6% were someone living alone who was 65 years of age or older. The average household size was 2.27, and the average family size was 2.89.[14]

In the city the population was spread out with 20.3% under the age of 18, 11.0% from 18 to 24, 30.6% from 25 to 44, 24.9% from 45 to 64, and 13.1% who were 65 years of age or older. The median age was 36.7 years. For every 100 females there were 96.0 males. For every 100 females age 18 and over, there were 94.0 males.[1]

For the period 2009–11, the estimated median annual income for a household in the city was $55,040, and the median income for a family was $69,980. Male full-time workers had a median income of $51,891 versus $36,167 for females. The per capita income for the city was $30,590. About 6.8% of families and 8.9% of the population were below the poverty line, including 13.2% of those under age 18 and 5.9% of those age 65 or over.[15]

The Dover School District consists of approximately 3600 pupils, attending Horne Street Elementary School, Garrison Elementary School, Woodman Park Elementary School, Dover Middle School and Dover High School. Dover High's athletic teams are known as The Green Wave, and the middle school's teams are The Little Green.

Saint Mary Academy, a Catholic school, has been in downtown Dover since 1912, currently serving around 200 students from pre-kindergarten to 8th grade. Many students at Saint Mary's subsequently attend St. Thomas Aquinas High School, a Catholic high school located on Dover Point.